348
FXUS63 KILX 270012
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
712 PM CDT Thu Jun 26 2025

.KEY MESSAGES...

- One more day of heat index values over 100 degrees will occur on
  Friday, but will mainly be limited to areas near and east of
  I-57.

- Rain chances will be minimal overnight (20-30% areal coverage),
  and mainly limited to the Illinois River valley. Chance of
  showers and thunderstorms will be higher on Friday and Monday
  with frontal boundary moving through.

&&

.UPDATE...
Issued at 712 PM CDT Thu Jun 26 2025

Most of the earlier convection has either moved out or faded away,
though a couple last gasps of showers/storms are east of I-57 this
hour. Main focus will be with the line of storms currently
extending from northeast Iowa into west central Missouri. Recent
high-res models have been showing some general weakening taking
place late evening as the storms cross the Iowa border, and
overnight rain chances will be focused near and west of the
Illinois River.

Most of the long-standing Heat Advisory was allowed to expire at 7
pm, with the segment near and east of I-57 continuing into early
Friday evening. Aside from a few early evening adjustments due to
cooler pockets from earlier showers, temperatures are on track.

Geelhart

&&

.DISCUSSION...
Issued at 235 PM CDT Thu Jun 26 2025

Continued the heat advisory until 7 pm today for central IL and
extended the heat advisory until 7 pm Friday from Danville to
Charleston/Mattoon to Effingham southeast. Heat indices should
peak from 100-107F through 7 pm with temps in the low to mid 90s
and dewpoints in the low to mid 70s. Heat indices are expected to
peak 100-105F in southeast IL on Friday afternoon and peak in the
90s over the remained of central IL. The high heat and humidity to
linger this weekend as heat indices peaking in the mid to upper
90s on Sat afternoon (highs near 90F) and 97-103F on Sunday
afternoon (highs in the lower 90s).

Radar mosaic shows isolated convection over central IL from the
IL river southeast to I-72 and southeast of I-70, lifting slowly
northeast. Unstable tropical airmass with ML CAPES 2-3k j/kg and
SB CAPES 3500-4200 j/kg. PW values of 1.6-1.8 inches. The main
synoptic frontal boundary was near the MN/IA border and southern
WI with 1009 mb low pressure near the MN/IA/SD border. SPC Day1
continues marginal risk of severe storms for damaging winds
northern half of CWA into early evening along with locally heavy
rainfall, similar to yesterday. As low pressure tracks to
northeast of Door County WI by 12Z/7 am Fri it will pull a cold
front se toward nw IL. This to bring chance of showers and
thunderstorms to the IL river valley late tonight into fri
morning. The front moves into northern cWA Fri night and then
lifts back into northern IL during Saturday. This to keep a chance
of convection around into this weekend, though chances will be
rather low over our area. More unstable tropical airmass lingers
over southeast IL Sat where higher pops will be.

Sunday we will see tropical air mass lift further northward over
IL so temps and dewpoints along with associated Heat Indices to be
a bit higher. Have 30-40% chance of convection Sunday afternoon
and evening. Cold front to then push back se over IL on Monday
likely bringing showers and chance of thunderstorms. We are
currently not in an outlook for severe storms by SPC on Monday
afternoon/evening but will need to be watched with front moving
into an unstable air mass. Highs Monday in the mid to upper 80s
with Lawrenceville around 90F where heat indices peak in upper 90s
in far southeast IL Mon afternoon. After a chance of convection in
southeast IL Monday evening, expect dry conditions returning
overnight Monday night through Wed night as weak high pressure
settles eastward into IL during mid next week. More seasonable
temps and humidity levels for early July return middle of next
week with highs in the mid to upper 80s and lows in the mid to
upper 60s.

07

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 615 PM CDT Thu Jun 26 2025

Main focus for any convection in the short term will be in the
06-09Z time frame, mainly KPIA-KSPI west, as a line of storms
currently well west of the Mississippi River moves east. However,
this is expected to fade some after midnight, with thunder chances
appearing minimal that far east. As we get into the heating of the
day on Friday, a cold front will be approaching KSPI/KBMI, with
any convection mainly ahead of it. Will include a PROB30 mention
of thunder chances from KSPI-KCMI.

Otherwise, VFR conditions expected to prevail at the terminals.
Ensembles try to bring some lower ceilings late morning with the
front, though these will generally be northwest of KPIA.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT Friday for ILZ046-056-057-062-063-
066>068-071>073.

&&

$$